The images also show fine in IE

One thing the article (Fix problems that cause images to not show) hasn't been updated to mention was Firefox's Tracking Protection feature, which could block some content in Private windows -- or in all windows if it has been turned on more generally. Check the left end of the address bar for a "shield" icon, and see this article for more information: What happened to Tracking Protection?.

I also recommend turning off the accessibility feature which blocks certain redirects, in case your mailing service uses a redirect in the process of retrieving an embedded image. You can do that here:

• Windows: "3-bar" menu button (or Tools menu) > Options
• Mac: "3-bar" menu button (or Firefox menu) > Preferences
• Linux: "3-bar" menu button (or Edit menu) > Preferences

In the left column, click Advanced. Then on the right side, with the "General" mini-tab active, make sure the following is not selected (box is not checked): "Warn me when websites try to redirect or reload the page"

Otherwise, you can try to diagnose the problem by checking Firefox's Network Monitor, which is one of the developer tools you can open in the lower part of the tab.

To display that, first open the message. Then open the Network Monitor using either:

• "3-bar" menu button > Developer > Network
• (menu bar) Tools > Web Developer > Network
• on Windows, Ctrl+Shift+q

Then reload the page in the upper part of the tab. The Network Monitor should display the various requests Firefox makes in the process of assembling the page, and the most common status codes on the left side are 200 Success, or 304 Unchanged (meaning the cached copy of the file was used). Do you notice any 400 or 500 statuses, or any items for which requests simply remain open without ever loading or getting a response of any kind?

Thanks, but

1. There is no shield icon, and 2. the "Warn me when websites try to redirect or reload the page" box is not checked

As for the status codes on the left of the Network Monitor, every single one is a 200. There are no 400 or 500 statuses.

Even so, I appreciate your help. Any other ideas?

When you were working on image permissions, did you use the Page Info dialog's Media list? To display that, either:

• right-click a blank area of the page and choose View Page Info > Media
• (menu bar) Tools menu > Page Info > Media
• click the padlock or "i" icon to the left of the site address, then the ">" icon, then More Information > Media

If you click in the box and then arrow down through the images, do you see the missing image anywhere? That would indicate that Firefox retrieved it but for some reason is not displaying it. If Firefox did not retrieve it, but the Network Monitor showed all successful retrievals, it would suggest that Firefox didn't even request it for some reason.

3 'images' come up in the Media list, but when I click on them they don't show up in the media preview box - see attached screenshot

Aha. Judging by the address, that's not the actual image requested, and instead the dialog indicates you are getting some text/html type content in place of the image.

To see what that HTML says, could you go back to the Network Monitor, click one of the matching lines, and then on the right side, change from Rules (or whatever panel is displayed) to Response. It could be an error message about the image not being found or not having permission to view it, or it might be something else.

Hi, I have tried the processes again today and this time the media list shows the images!! - see screenshot. They appear in the Network Monitor with a 304 code - see screenshot. So what does '304 Unchanged (meaning the cached copy of the file was used)' mean from your earlier post?

I hope this is a relatively straightforward fix. Even so, I'm concerned that none of my Firefox clients will go to this effort to view the missing images - instead they may just discard the email as looking unprofessional! At the moment I'm just hoping most of them viewed it fully in Chrome or IE

Also, the problem with the images isn't just limited to my own personal stock of images - the 'official' Mailchimp images (Mailchimp logo, Facebook button etc) also don't show.

If the image was found in the cache, then normally it would display just fine. To reload a page "fresh" bypassing the cache, you can use Ctrl+Shift+r and then the images should show a 200 status code.

Since Firefox has the images and you can confirm that through Page Info, the mystery of why they cannot be viewed in the message persists.

If you follow the link to view the message in a web browser, does it work on that page?

If you haven't already, could you test in Firefox's Safe Mode? In Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, and some other advanced features to help you assess whether these are causing the problem.

If Firefox is not running: Hold down the Shift key when starting Firefox.

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement? (More info: Diagnose Firefox issues using Troubleshoot Mode)

If this is in an email then the images might be embedded as Content-ID (src="cid:image"). Firefox doesn't support images embedded as src="cid:image". You need an email program to see images that are embedded this way.

Ok, so I've solved the problem - I could see the images normally in Safe Mode, and then by process of elimination (enabling one add-on at a time!) found the add-on 'Disconnect' to be the problem. Sorry to waste your time. I thought I'd turned off the add-ons previously when looking for a fix, but I don't think I then restarted Firefox. Doh.

One suggestion - on the 'Fix problems that cause images to not show' page, I'd add 'Open in Safe Mode' as a possible fix quite near the beginning of the table of contents. Anyway, sorry again - and thanks for your help, much appreciated!

No worries, I'm not terribly surprised that a bulk mailing company's content is blocked by an anti-tracking extension, it's just that we don't have insight into a user's set of extensions unless they post them, so we have to put all the work on you.

Sure. I've only got a short list of add-ons so I should have just posted them at the start - I'll bear that in mind should an issue arise in the future! Glad I can continue with Mozilla with confidence. Cheers